The CXC chemokines have recently emerged as key regulators of angiogenesis due to their ability to enhance the migratory capacity of endothelial cells and facilitate the homing of EPCs to ischemic tissues (1, 2). Stromal cell-derived factor-1-α (SDF-1α, also called CXCL12) is one of the most potent proangiogenic CXC chemokines. Both in vivo and in vitro data support a critical role for SDF-1α in angiogenesis. SDF-1α treatment of endothelial cells induces tube-like structure formation and migration (3, 4), and SDF-1α increases tubulogenesis of microvascular endothelial cells via enhanced expression of VEGF and FGF and subsequent endothelial cell migration (5). SDF-1α is required for angiogenesis associated with wound healing under conditions in which SDF-1α expression inversely correlates with oxygen tension (6, 7). Likewise, hypoxia-inducible factor (HIF-1)-induced SDF-1α expression in ischemic tissue increases the adhesion, migration and homing of circulating progenitor cells that express the SDF-1α receptor CXCR4, thereby promoting tissue regeneration (8).
Further evidence that SDF-1α acts as a key regulator of angiogenesis comes from observations that CXCR4, also called Fusin or leukocyte-expressed seven-transmembrane-domain receptor (LESTR), and its co-receptor CXCR7 are required for normal cardiac ventricular septum formation and vascular development (9-14). CXCR4 is selectively expressed in vascular endothelial cells and EPCs (8, 15), and its expression is induced by pro-angiogenic factors such as FGF2 and VEGF (16). Although the critical roles of SDF-1α/CXCR4 in endothelial cell migration are well recognized, relatively little is known about the signal transduction pathways that mediate these effects.
SDF-1α-induced EPC migration is mediated in part through activation of the PI3K/Akt/eNOS signal transduction pathway (17). However, the specific role of NO generated by eNOS in SDF1α-induced neovascularization is still poorly understood and the mechanism by which eNOS regulates SDF-1α-induced endothelial migration is not known. Here we characterize the participation of eNOS in the regulation of SDF-1α-mediated endothelial cell activation.